Ethanol dimer: Observation of three new conformers by broadband rotational spectroscopy

The conformational behavior of the hydrogen-bonded cluster ethanol dimer has been reinvestigated by chirped pulse Fourier transform microwave spectroscopy in the 2–8 GHz frequency region. Three new conformers (tt, tg+, and g−g+) have been identified together with the three (g+g+, g−t, and g+t) previously observed by Hearn et al. (2005) and their rotational and centrifugal distortion constants have been determined. By using different carrier gases in the supersonic expansion, the relative abundances of the observed conformers have been estimated. The monosubstituted 13C species and some of the 18O species of the most abundant conformers g+g+, g−t, and tt have been observed in their natural abundance, which led to the partial determination of their rs structures, and the r0 structure for the tt conformer. The six observed conformers are stabilized by the delicate interplay of primary OH···O and secondary CH···O hydrogen bonds, and dispersion interactions between the methyl groups. Density functional and ab initio methods with different basis sets are benchmarked against the experimental data.